Compounds containing metallic elements have hitherto been used as catalysts for various reactions. In liquid-phase reactions, compounds such as metal salts and metal complexes, among those catalyst compounds, are frequently used as catalysts in the state of being dissolved in the liquid reaction mixture (hereinafter, these compounds are referred to as “soluble metallic catalysts”). These soluble metallic catalysts generally are highly selective catalysts having high activity because they act in a dissolved state. However, since these catalysts are difficult to separate from the liquid reaction mixtures, they are discarded after use or require much labor or cost for separation/recovery.
An example of such liquid-phase reactions is a process for producing 2-hydroxyethyl acrylate by causing ethylene oxide to add to acrylic acid with the aid of a chromium compound as a soluble metallic catalyst. If the chromium compound in this process can be easily separated and recovered and be reused, considerable environmental and economical merit can be expected.
Various techniques are known for the separation/recovery of soluble metallic catalysts. Examples thereof include a method in which after a reaction the reaction product is taken out by distillation and the catalyst is recovered as a distillation bottom and a method in which a catalyst is recovered by an extraction operation. However, these techniques pose a problem concerning accumulation of a by-product, or necessitate complicated steps and enlarged apparatus, leading to a cost increase.
Also known is a technique in which an ion-exchange resin is used to recover a soluble metallic catalyst. Japanese Patent Laid-Open No. 44300/1984 discloses a method in which after phthalic acid is reacted with an epoxy compound with the aid of a chromium compound as a soluble metallic catalyst, the resultant liquid reaction mixture is dissolved in a solvent, e.g., water, and the catalyst is recovered with a cation-exchange resin. Although this method can be used for catalyst recovery, it has drawbacks that use of a solvent is necessary for the recovery and that a special eluent and much labor are required for reusing the catalyst adsorbed onto the cation-exchange resin.
Japanese Patent Laid-Open No. 152246/1999 discloses a method of catalyst recovery in a process for producing an aromatic carboxylic acid with the aid of a cobalt catalyst. This method uses a chelate type anion-exchange resin for the recovery. Although this method is effective in efficiently recovering the catalyst, a catalyst adsorption step which takes much time and a desorption step are necessary separately from the reaction step.
As described above, the related-art methods of catalyst recovery with an ion-exchange resin have had problems that the reuse of the catalyst adsorbed onto the ion-exchange resin necessitates much labor and that the process is complicated and requires much time because of the necessity of a catalyst adsorption step and a catalyst desorption step separately from the reaction step.
A process in which a combination of a zeolite, which is a solid acid catalyst, and a tin compound serving as a soluble metallic catalyst is used in the esterification reaction of octanoic acid with pentaerythritol is discussed in Heisei 10-nen Jisedai Kagaku Purosesu Gijutsu Kaihatsu Seika Hôkoku-sho, pp.395-422 (Japan Chemical Industry Association). In this process, the zeolite functions not only as a catalyst but as an adsorbent for the tin compound and, hence, the tin compound can be easily recovered/reused. However, this process is usable in limit applications because zeolites dissolve in strong acids or alkalis and because in some reactions, zeolites may cause undesirable side reactions, e.g., ring-opening polymerization of epoxy compounds, due to the acid sites thereof. Furthermore, since the adsorption of the tin compound onto the zeolite is not based on ion exchange, the tin compound adsorbed readily passes away upon cleaning with hexane. Consequently, the zeolite cannot be cleaned while keeping the catalyst held thereon and, hence, it has been difficult to produce a variety of products with the same catalyst system.
On the other hand, U.S. Pat. No. 4,069,242 (corresponding to Japanese Patent Publication No. 25421/1986) describes a process for producing an ester, e.g., 2-hydroxyethyl acrylate, in which a chromium (or iron) compound and an organic amine compound are used in combination as a catalyst. The use of these two catalyst compounds in combination in this process is intended to produce a synergistic effect in the rate of reaction and the yield of the target compound. There is no description therein concerning the separation/recovery of a soluble metallic catalyst with an anion-exchange resin. Although the Examples given therein contain a statement to the effect that an iron compound was used in combination with an anion-exchange resin, the degree of adsorption of the iron compound onto the anion-exchange resin is presumed to be below 50%. The actual effect of recovery in this related-art process is low.
Soluble metallic catalysts are usually discarded frequently. However, discard is undesirable from the standpoints of profitability and environment, and there is a desire for a method for easily recycling soluble metallic catalysts.
As described above, the recovery/reuse of a soluble metallic catalyst in various liquid-phase reactions in the related art has had drawbacks that much labor or a large equipment is required and the process is complicated and takes much time. Furthermore, the technique in which a soluble metallic catalyst and a zeolite are used in combination has been usable in limited applications because of the problems attributable to the nature of zeolites and because the metallic catalyst dissolves away upon cleaning.
Accordingly, the invention has been achieved in view of the problems of the above described techniques of the related art. An aim of the invention is to provide a method of reaction using a soluble metallic catalyst and an anion-exchange resin in which the soluble metallic catalyst can be efficiently used, recovered, and reused with great ease at low cost. Another aim of the invention is to provide a method of recovering the soluble metallic catalyst and a method of reusing the catalyst recovered.